It is now well known that relatively dimple-free tube end configurations can be realized in a guillotine type cutting operation wherein a notching apparatus cuts a shallow groove in the exterior tube wall transverse to the tube axis just prior to the entry of the severing blade tip into the notched portion of the tube wall. This notching function reduces or eliminates the tendency of the tube wall to collapse upon entry of the severing blade. The advantage of this "double-cut" operation lies in the reduction or elimination of secondary operations to restore the tube end to a round configuration.
The notching apparatus typically comprises a notching blade holder which is interconnected with the upper platen of the die set by way of a mechanical cam and cam follower such that the descent of the upper platen toward the tube causes the notching blade holder to travel through a transverse path across the tube; both thrust and "pull-across" motions are known. See, for example, U.S. Pat. Nos. 4,109,555, issued Aug. 29, 1978 and 4,294,147, issued Oct. 13, 1981.
Various blade configurations have evolved, some of which include hook portions and all of which include sharp points defined by intersecting blade edges to form the actual steel cutting area. Some of these blades are irregular in shape but are reversely symmetrical so that the same blade may be rotated 180.degree. to present a new cutting area when the first cutting area becomes dull and ineffective.